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By using the internal coordinates analysis method, determine the symmetry types

ID: 894802 • Letter: B

Question

By using the internal coordinates analysis method, determine the symmetry types for all of the normal modes of vibration for the molecule NH3. To which point group does it belong? First determine the transformation properties of the 3 bond stretching modes, deltad, and then transformation properties of the 3 angle bending, delta A, motions. Reduce the reducible representations to their irreducible components to give the symmetry types of the normal modes. How many vibrational modes are there in all?

Explanation / Answer

The NH3 molecule belongs to the C3v group.

No.of vibrational modes = 3N - 6 , where N = no.of atoms

=> No.of vibrational modes in NH3 molecule = 3(4) - 6 = 6